Details about the designations and classifications of previous 1-hour ozone nonattainment and maintenance areas can be found here.

On June 8, 2007, the United States Court of Appeals vacated the Subpart 1 portion of the Phase 1 Rule (Court Order) (PDF).
On May 14, 2012, the Former Subpart 1 nonattainment areas were classified under Subpart 2
(77 FR 28424
) (PDF), effective June 13, 2012.